python中[:-1]

python中[:-1]:
It slices the string to omit the last character, in this case a newline character:

>>> 'test\n'[:-1]'test'

Since this works even on empty strings, it’s a pretty safe way of removing that last character, if present:

>>> ''[:-1]''

This works on any sequence, not just strings.

a[-1]    # last item in the arraya[-2:]   # last two items in the arraya[:-2]   # everything except the last two items

>>> seq[:]                # [seq[0],   seq[1],          ..., seq[-1]    ]>>> seq[low:]             # [seq[low], seq[low+1],      ..., seq[-1]    ]>>> seq[:high]            # [seq[0],   seq[1],          ..., seq[high-1]]>>> seq[low:high]         # [seq[low], seq[low+1],      ..., seq[high-1]]>>> seq[::stride]         # [seq[0],   seq[stride],     ..., seq[-1]    ]>>> seq[low::stride]      # [seq[low], seq[low+stride], ..., seq[-1]    ]>>> seq[:high:stride]     # [seq[0],   seq[stride],     ..., seq[high-1]]>>> seq[low:high:stride]  # [seq[low], seq[low+stride], ..., seq[high-1]]